The cephalosporins are an important group of antibiotics which have the unfortunate occasional side-effect of producing nephrotoxicity. Cephaloridine produces a proximal tubular necrosis which is prevented by probenecid. Renal cortical cephaloridine uptake by the p-aminohippurate secretory transport carrier is substantially greater than that of p-aminohippurate and other nontoxic cephalosporins. Studies in this laboratory involve: the toxicity of cephaloridine to mitochondrial and tubular cell respiration; the toxic interaction of the cephalosporins and the aminoglycosides in the kidney; the effects of inhibitors of cytochrome P450 oxidase activity on cephaloridine toxicity; and the relationship between the transport and the nephrotoxicity of the newer cephalosporins.